Conventionally, as a technology for a driving circuit for a display device such as TFT liquid crystal display, the technology for a driving circuit disclosed in U.S. Patent Publication No. 2005-052477 (JP-A No. 2005-99665) has been known. This driving circuit has gray scale voltage lines in accordance with the number of gray scales of high-order bits of display data, a selector which receives a pulse signal at each time determined in advance so as to correspond to low-order bits of the display data and selects a gray scale voltage line in accordance with the contents of the high-order bits to output the voltage to a signal line only during the period when the pulse signal is kept active, and a gray scale voltage generating unit for supplying a gray scale voltage, which is changed by the number of gray scales of low-order bits of image data, to each gray scale voltage line. In the driving method disclosed in U.S. Patent Publication No. 2005-052477, one gray scale voltage is selected from a gray scale voltage group whose voltage levels are changed every predetermined divided period in accordance with a high-order bit of display data, and the selected gray scale voltage is outputted to a signal line only during the period in accordance with the information of a low-order bit of the display data. This method is hereinafter referred to as a first driving method. According to the configuration and operation described above, it is possible to realize more gray scale displays in smaller circuit scale.
Moreover, as a conventional method for realizing the γ adjusting function, the driving circuit disclosed in JP-A No. 2005-49868 has been known. In the circuit and method thereof, amplitude adjustment, slope adjustment, and fine adjustment for an S-shaped γ-characteristic curve can be made by an amplitude adjustment register, slope adjustment register, and fine adjustment register so that each gray scale voltage corresponding to a desired γ-characteristic in the characteristics of each liquid crystal panel can be adjusted.